Piezocrystal device



Feb. 17, 1942. M. KLEIN PIEZOCRYSTAL DEVICE Filed Aug. 22, 1940 3Sheets-Sheet 1 INVENTOR Feb. 17, 1942. M. KLElN 2,273,711

` PIE'zocRYsTAL DEvIcE Filed Aug. 22. 1940 a sheets-meet 2.

BY fyi-5M i Feb. 17. 1942. MKM-:1N

PIEZOCRYSTAL DEVICE Filed Aug. 22. 1940 3 Sheets-SheetI 3 Tl-l lNVENTORM Patented Feb. 17, 1942V Mark-mein, musmng, N. Y.,

Crystal Laboratories,

Inc., corporation of New York assignor to Premier New York. N. Y., a

ApplicationAugust 22, 1940, Serial No. 353,643

l 14 Claims.

This invention relates to piezo crystal devices and more especially toimprovements in temperature-controlled piezo crystals.

A principal object of the invention. is to provide an improved manner'ofretaining a piezo crystal of the adjustable air gap type.

Another object is to provide an improved holder and housing for a piezocrystal unit designed to bemaintained at alconstant internal temperatureover a wide range of external or ambient temperatures, and one which is'capable of reliable operation and maximum stability under extremelyunfavorable climatic and service conditions. As a result the deviceaccording to the invention is well suited for use on mobile craft suchAas aeroplanes, naval/or marines ves-- sels, and in fact any situationwhere exposure to dust, moisture or extremes `of temperature andvibration constitute a severe handicap to crystal stability. v

' Another object is to provide an improved temperature-controlled holderfor piezo crystals of the contact type as well as those of the air gaptype.

Another object is to provide an improved piezo crystal housing of theplug-in type having specially designed means to connect with theungrounded electrode either at the top of the housing or through one ofthe prongs.

A feature ofthe invention relates to an improved heat insulating andmoisture-proof housing for a piezo crystal device.

Another feature relates to a piezo crystal housing and assembly wherebythe crystal unit proper can be assembled and tested as a completeunitary assembly either within or independently of thetemperature-controlled housing. As a result of this feature the crystalunit proper is readily assembled and removed from the housing asconditions may require.

'A further feature relates to a piezo crystal unit and atemperature-controlled insulating housing with a pronged plug-in basl,the housing being constructed in a plurality ,of parts for easytelescoping assembly and with a minimum of heat conduction from thecrystal proper to the socket into which the unit isplugged. i

Another feature relates to a piezo crystal holder which in itself issealed-and provided with a lling of inert gas, the holder being alsoenclosed in a heat insulating housing having a pronged plug-in base, thesaid housing being likewise provided with a filling vof an inert gas andbeing moisture-proof and dust-proof.

A further feature relates to an improved contacting arrangement betweena crystal electrode and an external prong or cap carried by a heatinsulating housing "within which the crystal vunit is enclosed.

A further feature relates to aso-called sandwich type piezo crystal unitand a heat insulating housing, together with a thermometer supported onthe housing and extending into the body of one of the crystal electrodeswherebythe temperature of the crystal may be more accurately indicated.

A further feature relates to a spring clamped crystal having speciallydesigned spacing guides for retaining the coiled clamping springs inaxial parallelism thus insuring that the clamping action is alwayssubstantially perpendicular to the face of the crystal.

A still further feature relates to the novel organization, arrangementand relative location and inter-connection of parts which constitute animproved and easily assembled temperature- I controlled piezo crystaldevice.

Otler features and advantages not specifically enumerated will beapparent after a considera- ,tiony of the following detaileddescriptions and the appended claims.

While the inventive concept will be disclosed A herein in certainpreferred embodiments, it will be understood that this is done merelyfor ex- Dlanatory purposes and not by way of limitation A thereto.Accordingly in the drawings,

connections to the varios Ament on the type Fig. 1 is a central verticalsectional view through a crystal holder 'and housing embodying featuresof the invention.

Figs. 2, 3, 4 and 5 are horizontal sectional views of Fig. 1 takenrespectively along the lines 2+2, 3 3, 4 4 and 5-5 viewed in thedirection of the arrows.

Fig. 6 is another view of Fig. 1 partly in section and showing amodification of the manner oi' making contact to the upper electrode ofthe crystal holder.

Fig. 7 is an external assembled view of Fig. l.

Fig. 8 is a composite diagram representing a Y ttom view of Fig. 1 andthe schematic` circuit prongs.

Fig. 9 is a detailed view of the thermometer protective housing andsupport.

Fig. 10 is an enlarged detailed view of one of the crystal' resilientclamping devices.

Fig. 11 shows the housing of Figs. 1 and 6 but with a crystal unit ofthe contact type.

Fig. l2 is an exploded view oi' the more important sections of thedevice to show the manner in which they are assembled. Fig. 13 is anexploded view showing the relation between th crystal and the retainerinsert of Fig. 1.

The invention .is in the nature of an improveof device disclosedinPatent general the device according designed to reduce the manu- No.2,131,826. In to the invention is and rendering with a maximum ofindependence of outside temperature Aand pressure conditions. In priordevices where the greatest stability is required, elaborate arrangementshave been provided in the form of `crystal ovens with thermostatcontrols which. while suitable for stationary use. are not verypractical for mobile use such as in aeroplanes, naval vessels, tanks andthe like because of the bulk and considerable weight of lthe partsnecessary to control the stability. The `device acording to the presentinvention represents an attempt to approximate if not entirely equal thestability of such prior oven controlled units. while allowing the'device to be used under practically all kinds of service conditionswhether mobile or stationary.

Referring to Fig. 12, the device comprises in general five sectionsconsisting of a base section I having a plurality of downwardlydepending rigid contact prongs fastened therein; a spacing collar 2; athermostatically controlled heater l; a crystal unit 4 including aholder containing a piezo crystal with its adjusting means; and a heatinsulating casing 5. These parts are so designed and proportioned thatby removing a minimum number of fastening screws, each of the sectionscan be rapidly disassembled and conversely they can be rapidlyassembled. Furthermore, the parts I, 2 and 5 are preferably fashionedout of ran insulating material of low dlelectric loss such for exampleas a phenolic material such as Bakelite The parts are fitted together soas to provide a moisture-proof and` dust-proof enclosing housing and onewhich is eectively gas-tight. As shown more clearly in thecross-sectional view of Fig. 1, the casing sec-4 tion l isdouble-walled, the outer wall 6 being sufilciently long to overlap therim of base section I when the device is completely asesmbled.

t The inner wall 'I is spaced from the outer wall by means of an annularblock 8 of similar insulating material. Preferably the parts 6, 1 and 8are fitted tightly together and if desired a layer of water-proof cementor lacquer may be used to render the joints gas-tight andmoisture-proof. The base section I is fastened to the block 8 by aseries of screws 9, the heads of which are recessed below the bottomsurface of the base, these recesses being filled with wax or othersuitable means to act as a telltale should the device be tampered withafter final assembly and test. Preferably a rubber or similarwater-tight, cornpressible gasket II) is located between the abuttingends of member 1, 8. and base I. Base I is provided on its inner facewith a circular recess into which is tightly fitted and preferablycemented a thin walledcylindrical member II also of insulating materialsimilar to parts 6 and 1. insulating material I2 is seated in the recessin base I and is held in place by a disc I3 of insulating material suchas Bakelite." The disc I! has two perforations, one to provide a passagefor the mutually insulated flexible conductors connecting the severalprongs to the various internal parts as schematically shown in Fig. 8.the other perforation allows the shank Il (Fig. 6) of one of the prongsto pass therethrough for purposes to be described.

The crystal unit l is a self-contained one,

forming a gas-tight holder and housing for the crystal I5. This holdercomprises in general a thick metal base I6 of aluminum, duralumin orother non-corrodible light-weight metal alloy; a top metal cover I1 ofthe same metal; and an member I1.

A layer of felt or other suitable heat,

than the crystal so that the crystal can be readily deposited therein.Preferably the abutting surfaces of member I8, I1 and IBV are machined,ground or lapped so that when they are tightly fastened together theyform an effective gas-tight seal as described in application Serial No.346,101. The member I8 constitutes one of the crystal electrodes andpreferably its inner surface is provided with a circular shallow recessI1* (Fig. i3) so that the crystal I5, which is rectangular or square,rests on the unrecessed corner portions Ill of electrode i5. and themajor portion of the crystal area is slightly spaced from the bottoni ofthe recess I1". The crystal is resiliently held iny place by a square orrectangular insert I9 oi ceramic having lateral dimensions approximatingthose of the crystal. The insert I9 has its underface undercut so as toprovide four raised corners 20 corresponding in shape to the cornerportions IB, Insert I9 is also provided with a circular opening 2i whichis slightly larger in diameter than the diameter of the adjustableelectrode 22. The member I9is maintained in contact with the crystalcorners by means of four spring-pressedretainers, one of which is shownin an enlarged form in Fig. 10. Each retainer comprises a metal rod 23which is threaded into Slidably tlescoped on rods 22 are respectivetubular metal members or eyelets 24 each of which has a flange 25 at itslower end. A coiled compression spring 26 surrounds members 23 and 24,one end of the spring engaging the member I1 and the other endvengagingthe flange 25. Thus the spring 26 maintains the flange 25 resiliently inengagement with the corner portions of member I8 to resiliently clampthe crystal at its corner portions only between electrode IB and memberi9. By this arrange ment. the crystal is resiliently clamped and anydistortion of the springs 26 does not effect the direction or effect ofthe clamping pressure since the pressure is transmitted to the member I9by flanged member 2l. By reason of the telescoping relation betweenmembers 23 and 24, the latter is constrained to move substantiallyentirely in a direction perpendicular to the crystal face.

The adjustable electrode 22 has one end threaded into a correspondingthreaded opening in member I1 and is locked in place by a thin metallocking disc 23* which is likewise threaded into the said opening. Theupper end of electrode- I1.has' a slot 2l'L to receive a screw driver sothat the electrode can be turned to vary the width of the air gapbetween the lectrode and the upper surface of crystal I5. owever, thelocking disc- 23' is preferably provided with a specially shaped opening25a so that a special tool is required to unlock the disc beforeelectrodes canl be adjusted, This tends to prevent unauthorizedadjustment of the electrode. Preferably, electrode I1 has a peripheralridge lIl which is larger in outside diameter than the l trode I8, andis ing 3I `-the bottom of electrode IB by means of screws 28. Thesection .3 comprises a circular block 30 preferably of the same metal asmetal 4elecprovided with a transverse openin which is located thethermostat 32 and the thermostat contacts 33, 34. vThe block 38 issurrounded by a heater 35 comprising a resistance wire wound around .aflexible insulator (form 38 which is attached to member 30 by screws 31.Preferably, the resistance wire and form are imbedded in a ceramicinsulator and as a further precaution against short circuits, a strip ofmica 38 `is positioned between the block 30 and the heater. The ends oithe heater wire are connected to the terminals 39 and 40 (Fig. 8). Oneterminal of the heater resistance is connected to the adjustablethermostat contact 34 and thence III 3 insulated casing is evacuated andprovided with a lling of an inert v"gas at approximately atmosphericpressure or higher than atmospheric pressure. This gas filling may beeffected through any opening which is later sealed.

In order that the temperaturev of the crystal may be accuratelyindicated, the body of eleca passage 6I and loangled thermometer. Thevertical arm 63 of this thermometer is located exteriorly of the casingand extends upwardly parallel thereto as shown more clearly in Fig. 7.For the' purpose of supporting the thermometer and protecting it againstbreakage there is provided a special form of protective housingconsisting of a channel- .shaped metal member 64 having av cut-out porbyan insulated lead wire 4I to prong 42 (Fig.

8). The other terminal of the heater resistance is connected byinsulated wire 43 to prong 44; and the other contact 33 of thethermostat is connected by insulated wire 45 to prong 46.- All theprongs vwith the exception of prong 41 (Figs. 6 and 8) are staked andfastened in thebase I, whereas prong 41 is the grounding prong and'passes freely through the base I and thence through the insulation I2and disc I3. 'Ihe upper oi' shank end I4 of this grounding prong isthreaded into a corresponding threaded opening 41a in member 30. Bytightening prong 41 the sections 3 and 4 are held in place, andpreferably the lower peripheral edge of electrode I6 is shouldered so asto fit within the upper en cl of the collar 2. Thus the prong 41 notonly acts as a grounding prong but also acts to support ,the sections 3and 4 within the heat insulated casing. The upper electrode 22 isconnected to prong 48 while the lower electrode I 5 is grounded throughprong 41.'

Tightly fitted within the upper end of wall member 1 is` a, shoulderedinsulator cap 48.. `Cap 43 has a central opening in axial alignment withthe crystal section 4. Threaded into the opening in member 49 is a metalbushing 50 which is provided with a shoulder 5I engaging theundersurface of member 49, the bushing being fastened in place by athreaded nut 52. Likewise the top cover 53 of the insulator casing isprovided with a central threaded opening to receive a threaded bushing54.- Interposed between bushing 54 and the shoulder in cover 53 is amoisture-proof gasket 55. Bushing 54 also carries an upwardly extendingmetal contact cap 56. The shank 51 of the bushing isprovided with ashoulder against which is seated one end of a coil spring 58. The otherend of the spring 58 engages a flanged tubular metal member or eyelet 53which is adapted to pass through the disc 23 to engage the member I1.Consequently the eyelet 59 is maintained in spring-pressed electricalcontact with the member I1 and thus with the upper electrode '25. Thespace between the cap 49 and the cap 53 is filled with a layer 60 offelt or other suitable heat insulating mation 65 to expose thegraduations on the thermometer 83. The member 64 is provided, adjacentitsupper end, with a right-angle flange I5 by means of which it may befastened by a suitable screw to the top cover 53. The lower end ofmember 64 is provided with a metal nipple 51 which is adapted to receivea compressible gasket 68. As shown more clearly in Fig. 4, the gasket 68is tapered and can be forced'into an opening in the wall 6 so as to sealthe wall against gas leakage. It will be understood of course opening inthe locking terial, thus completing the insulation of lthe casing. I

Should for any reason it be desired to adjust or test the frequency ofthe crystal unit without removing it from the casing, all that isnecessary is to unscrew the bushing 54 whereupon an ad justing tool maybe inserted through the opening in cap 53 to unlock the disc 23a andthen to adjust the electrode I1. After the parts have been finallyassembled, adjusted and tested, the

that a corresponding aligned opening is provided on the inner wall 1 sothat the section 62 of the thermometer can be passed into the passage 6Iand the electrode Il.

In the embodiment of Fig. 1, the upper electrode 22 of the crystal unitis connected into circuit through the top contact cap 56. In certaininstallations, it may be advisable to have all the connections madethrough the base. For this purpose, there is attached to the lower endof bushing 50 (Fig. 6) a frusto-conical or nested coil spring 'I I thelower and wider turns of which press against the member I1. A metalWasher 12 is fastened beneath nut 52 and a wire 13 is fastened to thesaid washer and leads downwardly to connect with an internally threadedmetal bushing 14 secured in insulator blocks 8. A screw 15 passesthrough base I to make contact with bushing 14 and this screw isconnected by Jconductor 16 to the prong 48. The remaining parts of Fig.6 corresponding to those of Fig. 1 bear the same designation numerals.However, in order to preserve the gas-tight character of the housing,the cap contact 58 of Fig. l is'removed and replaced by a threadedinsulator closure bushing 11.

In the-foregoing embodiments, the crystal unit is of the air-gap type,but it will be understood of course that the crystal unit may be of thesocalled contact type. Thus, as shown in Fig. 1, such a unit is shown inFig. 11 and parts corresponding to those of Fig. 1 bear the samedesignation numeral. In this embodiment, the crystal is of the lowfrequency type and is adapted hto rest directly on the electrode 8|. Themember I1 may be the same as the corresponding member of Fig. l but theceramic member -82 instead of trode 84 which has a recess 85 in which isseated threaded metal plug Il which is'threaded into the member I'I andlocked in place by the locking disc 23. A flexible metal wire 88connects the electrode Il to the member l1. By reason of the tapered endl of member 8l engaging the bottom of recess Il, the electrode Il restsflat j' against the upper face of crystal Il. Consequently, the memberl1 may be turned without disturbing the contact relations lbetween thecrystal Il and the electrode 8l. For a detailed description of this typeof crystal holder, reference may be had to application Serial No.346,101, filed July 18, 1940. The remaining parts of Fig. 11 are thesame as those of Fig. 1 and Fig. 6 and further detailed descriptionthereof is not deemed necessary. In order to insure the gas-tightness ofthe outer casing suitable compressible gaskets il are provided aroundeach' of the contact prongs where they engage the base I.

What I claim is:

1. In a piezo-crystal device, a heat insulated gas-tight casingcomprising tubular inner and outer members, end closure members for theouter casing and joined thereto in a gas-tight manner, one o! saidclosure members carrying a plurality of rigid contact prongs, aremovable closure plug in the other closure member, a unitary assemblyof piezo-crystal and holder mounted within said casing, said unitaryassembly having 'a frequency adjusting member in alignment with saidplugwhereby said crystal can be adjusted without removing it from thecasing.

2. A piezo-crystal device according to claim 1, in which said plug has aportion extending through said other closure member and carries aspring-pressed contact for completing the electrical connection to oneof the electrodes of said unitary assembly.

3. A piezo-crystal device comprising an insulator base carrying aplurality of rigid contact prongs, a tubular spacer member carried bysaid base, a unitary assembly of piezo-crystal and holder supported onthe edge of said spacer member. and a gas-tight heat insulated housingtelescoped over said unitary assembly and said spacer and fastened tosaid base.V

4. A piezo-crystal device according to claim 3 in which a right-angledthermometer is supported on said'casing with the bulb portion extendingthrough the said casing and into the body of one of the crystal holderelectrodes.

5. A piezo-crystal device comprising a crystal holder including a hollowceramic member closed at its upper and lower ends by metal members todefine a crystal chamber, a crystal supported within said chamber, asubstantially completely heat-insulated casing enclosing said holder, apassage in the body of said lower end closure member, an opening in thewall of said casing in alignment with said passage, a rightangledthermometer' having the bulb portion extending through said opening intosaid passage, and having its indicator portion extending outwardly ofand along said casing, and a protective. housing for said indicatorportion, said housing being rigidly fastened to said casing.

6. A piezo-crystal device according to claim 5 in which a gas-tightgasket is provided around the` portion of the thermometer as it passesthrough said casing.

7. A piezo-crystal device according to claim 5 a tapered projectioncarried by the screwin which said lower end closure member constitutesone of the crystal electrodes upon which the crystal rests, and apassage is provided therein underneath the crystal and in closeproximity thereto, the bulb portion of said thermometer being located insaid passage.

8. A piezo-crystal holder comprising'a tubular ceramic member, metalclosure plates fastened to opposite ends of said member to denne acrystal chamber, the lower one of said closure plates being a crystalelectrode, a shallow recess in the face of said electrode, apiezo-crystal resting on the marginal edge of said recess, a removableceramic insert in engagement with said crystal, a plurality ofspring-pressed members engaging said ceramic insert to press itresiliently against the crystal, and an electrode adjustably mounted inthe upper one of said closure plates to define.

an adjustable air gap above the crystal.

9. A holder according to claim 8 in which said adjustable electrode isprovided with a marginal ridge for preventing complete removal oi' theadjustable electrode without substantially disassembling said holder.

10. A holder according to claim 8 in which said ceramic insert hasraised corner portions whereby only marginal portions of the crystal arecontacted thereby, said insert being provided with a central opening toallow said adjustable electrode freely to pass into close proximity to.

said crystal.

11. A piezo-crystal holder comprising a pair of crystal electrodes, apiezo crystal located between said electrodes and upon one of which saidcrystal rests, and resilient means to press said crystal against saidelectrode comprising a plurality of pairs of telescoped members, aspring for each pair of telescoped members and normally tending to pressone of said telescoped members towards said crystal.

12. A piezo-crystal holder comprising a pair of spaced metal membersbetween which a crystal is located, a plurality of rods carried by oneof said metal membersfa tubular member slidably telescoped on each rodwith its lower end adapted to clamp the crystal against the other ofsaid metal members, and a spring for normally tending to press saidtubular member towards the crystal.

13. A piezo-crystal holder comprising a pair of spaced metal platesbetween which a crystal is located, a plurality of rods carried by oneof said metal members, a tubular member slidably telescoped on each ofsaid rods, a compression spring. surrounding each rod and engaging theassociated tubular member, a ceramic insert having its corner portionsresting on the crystal, said corner portions being resiliently engagedby said tubular metal members.

14. A piezo-crystal device comprising a unitary assembly of crystal andcrystal holder with the crystal chamber defined by a tubular ceramicmember closed at opposite ends by metal.plates one of which acts as acrystal electrode, said holder being evacuated and provided with afilling of an inert gas, a heater-thermostat controlr assembly removablyfastened to said iirst assembly, a substantially completely heatinsulated and gas-tight casing enclosing said assemblies, said casingbeing evacuated and provided with a filling of an inert gas.

MARK KLEIN.

